Roller bearing

ABSTRACT

A roller bearing capable of effectively restraining occurrence of smearing or the like is provided. A cylindrical roller bearing includes: an outer ring having an outer ring raceway surface; an inner ring having an inner ring raceway surface that faces the outer ring raceway surface; and a plurality of cylindrical rollers rollably disposed between the outer ring raceway surface and the inner ring raceway surface. The inner ring raceway surface of the inner ring is provided with a manganese phosphate coating, and a rolling contact surface of each cylindrical roller is provided with a diamond-like carbon coating.

TECHNICAL FIELD

The invention relates to a roller bearing for use in a wind-powered generator or the like.

BACKGROUND ART

As bearings disposed in, for example, gear boxes for wind-powered generation, medium-size roller bearings are often used. There are some cases where a windmill for use in wind-powered generation is placed in a non-steady operation which is other than a normal power-generating operation and in which rotary torque is not transmitted to a speed increaser, when electric power is cut off due to electricity outage or the like, when a control of reducing the rotary torque is performed due to high wind or the like, etc. In such a case, especially, a roller bearing mounted on a high-speed shaft rotates at a high speed in a nearly non-load state, so that a raceway surface of the bearing is not supplied with sufficient lubricant and therefore smearing (a phenomenon in which a plurality of minute seizures is generated) occurs on a raceway surface of a rotary ring or rolling contact surfaces of rollers, resulting in a reduced service life of the roller bearing.

Therefore, conventionally, in order to protect the raceway surface of the rotary ring and the rolling contact surfaces of the rollers, the raceway surface and the rolling contact surfaces are subjected to a surface treatment with manganese phosphate coating (see, for example, Patent Document 1).

PRIOR ART DOCUMENT Patent Document

-   -   Patent Document 1: Japanese Patent Application Publication No.         2003-156053

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

However, the manganese phosphate coating is inferior in load bearing, and therefore has a problem that peeling easily occurs on the raceway surface or the rolling contact surfaces. In order to solve this problem, it is conceivable to form a diamond-like carbon (DLC) coating that is excellent in load bearing, instead of the manganese phosphate coating, on the raceway surface or the like. However, in this case, the friction coefficient is smaller, and therefore there occurs a problem that slippage more easily occurs between the raceway surface of the rotary ring and the rolling contact surfaces of the rollers and, therefore, occurrence of smearing cannot be sufficiently restrained.

The invention has been made in view of the foregoing circumstances, and it is an object of the invention to provide a roller bearing capable of effectively restraining occurrence of smearing or the like.

Means for Solving the Problem

The roller bearing of the invention for achieving the foregoing object is characterized by comprising: a fixed ring having a fixed raceway surface; a rotary ring having a rotary raceway surface that faces the fixed raceway surface; and a plurality of rollers rollably disposed between the fixed raceway surface and the rotary raceway surface, wherein, out of the rotary raceway surface and a rolling contact surface of each of the rollers, one of the surfaces is provided with a manganese phosphate coating and the other surface is provided with a diamond-like carbon coating.

According to the invention, out of the rotary raceway surface of the rotary ring and the rolling contact surface of each roller, one of the surfaces is provided with a manganese phosphate coating that is inferior in load bearing but greater in friction coefficient, and the other surface is provided with a diamond-like carbon coating that is small in friction coefficient but excellent in load bearing. That is, since the rotary raceway surface and each rolling contact surface are provided with two kinds of coatings that cover each other's shortcomings, the manganese phosphate coating that is great in friction coefficient makes slippage between the rotary raceway surface and the rolling contact surface of each roller less likely to occur, so that occurrence of smearing can be effectively restrained. Furthermore, since the diamond-like carbon coating which is excellent in load bearing hardens the surface, occurrence of peeling on the surface provided with the coating can be effectively restrained.

Furthermore, it is preferable that, in the roller bearing, the one of the surfaces be the rotary raceway surface and the other surface be the rolling contact surface of each roller.

In this case, since the rotary raceway surface is provided with the manganese phosphate coating, which is great in friction coefficient, the friction force on the coating makes it possible to efficiently transmit rotary drive force of the rotary ring to the rollers.

Furthermore, it is preferable that, on the rotary ring, a rib surface that is in sliding contact with an end surface of each roller be provided on at least one side of the rotary raceway surface in an axial direction, and that, out of the rib surface and the end surface of each roller, one of the surfaces be provided with the manganese phosphate coating and the other surface be provided with the diamond-like carbon coating.

In this case, since the rib surface of the rotary ring and the end surface of each roller are also provided with two kinds of coatings that cover each other's shortcomings, due to the manganese phosphate coating, which is great in friction coefficient, the rollers are more likely to be rotated together with the rotary ring by the sliding contact resistance between the rib surface and the end surface, so that rotary drive force of the rotary ring can be more efficiently transmitted to the rollers. Furthermore, since the diamond-like carbon coating, which is excellent in load bearing, hardens the surface, occurrence of peeling on the surface provided with the coating can be effectively restrained.

Effects of the Invention

According to the roller bearing of the invention, it is possible to effectively restrain occurrence of smearing or the like by performing a surface treatment with coating, thereby increasing the service life.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is sectional view showing a roller bearing according to a first embodiment of the invention.

FIG. 2 is a graph showing results of an endurance test of coatings.

FIG. 3 is a schematic diagram showing a testing device for the aforementioned endurance test.

FIG. 4 is a graph showing transitions in friction coefficients of coatings.

FIG. 5 is a schematic diagram showing a measuring device for measuring transitions in the friction coefficients.

FIG. 6 is a sectional view showing a roller bearing according to a second embodiment of the invention.

MODES FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the roller bearing according to the invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view of a roller bearing according to a first embodiment of the invention. The roller bearing according to the present embodiment is a cylindrical roller bearing 1 that bears a radial load in a gearbox for wind-powered generation. The cylindrical roller bearing 1 includes an outer ring 2 as a fixed ring, an inner ring 3 as a rotary ring that is disposed so as to be rotatable coaxially with the outer ring 2, a plurality of cylindrical rollers 4 that are rollably disposed between the outer ring 2 and the inner ring 3, and a cage 5 for holding the cylindrical rollers 4 at predetermined intervals in circumferential direction.

The outer ring 2 has an outer ring raceway surface (fixed raceway surface) 2 a that is formed on its inner periphery, and rib portions 2 b formed to be protruded radially inward at axially opposite sides of the outer ring raceway surface 2 a. Each rib portion 2 b has a rib surface 2 b 1 that is in sliding contact with a corresponding one of end surfaces 4 b of each cylindrical roller 4 at the axially opposite sides thereof.

On the outer periphery of the inner ring 3, there is formed an inner ring raceway surface (rotary raceway surface) 3 a that faces the outer ring raceway surface 2 a of the outer ring 2. The cylindrical rollers 4 are rollably disposed between the outer ring raceway surface 2 a and the inner ring raceway surface 3 a. An outer peripheral surface of each of the cylindrical rollers 4 is a rolling contact surface 4 a that rolls on the outer ring raceway surface 2 a and the inner ring raceway surface 3 a.

The cage 5 includes a first annular portion 5 a and a second annular portion 5 b that are disposed apart from each other in the axial direction, and a plurality of pillar portions 5 c that are disposed at equal intervals in the circumferential direction of the two annular portions 5 a, 5 b and that connect the two annular portions 5 a, 5 b. Pockets 5 d are formed between the two annular portions 5 a, 5 b and the adjacent pillar portions 5 c. The cylindrical rollers 4 are disposed in these pockets 5 d. The cage 5 retains, in the plurality of pockets 5 d, the plurality of cylindrical rollers 4 at predetermined intervals in the circumferential direction.

The outer ring raceway surface 2 a of the outer ring 2, the inner ring raceway surface 3 a of the inner ring 3 and the rolling contact surface 4 a of each of the cylindrical rollers 4 are surface-treated with respectively different coatings. Specifically, on each of the outer ring raceway surface 2 a and the inner ring raceway surface 3 a, there is formed a manganese phosphate coating 6 a that extends over the entire circumference of the raceway surface. Furthermore, on the rolling contact surface 4 a of each cylindrical roller 4, there is formed a diamond-like carbon (DLC) coating 6 b that contains, for example, tungsten carbide carbon (WCC) and that extends over the entire circumference of the roller. The film thickness of each manganese phosphate coating 6 a and each diamond-like carbon coating 6 b is set equal to or less than 3 μm.

FIG. 2 is a graph showing results of an endurance test that was conducted until occurrence of peeling of the manganese phosphate coating and the diamond-like carbon coating.

Conditions of this endurance test are as follows. A first test piece is a test piece in which a manganese phosphate coating is formed on a flat-plate test piece made of JIS SUJ2. Furthermore, a second test piece is a test piece in which a diamond-like carbon coating is formed on a flat-plate test piece made of JIS SUJ2.

A method of the endurance test performed until peeling occurred on the manganese phosphate coating of the first test piece will be shown below.

FIG. 3 is a schematic diagram of a testing device for the endurance test. This testing device includes an inner ring 21 for an axial bearing which is made of JIS SUJ2 and which has an annular raceway 21 a, six balls 22 of ⅜ inch made of JIS SUJ2, an annular cage 23 that holds each of the balls 22, lubricating oil 24, and a container 25 in which the first test piece 30 is disposed and the lubricating oil 24 is stored. The annular raceway's diameter (the diameter of a groove bottom of the raceway 21 a, P.C.D.) is φ38 mm.

The first test piece 30 was placed in the container 25 so that the manganese phosphate coating 31 (corresponding to the manganese phosphate coating 6 a according to the invention) faced upward in the vertical direction, and the six balls 22 held by the cage 23 were placed on the manganese phosphate coating 31, and the inner ring 21 was put on the six balls 22 so that the balls 22 were placed within the raceway 21 a. The lubricating oil 24 was put into the container 25 so that the first test piece 30 was completely submerged and the cage 23 was immersed up to its substantially middle position in the vertical direction. As the lubricating oil 24, MEROPA WM320 in trade name (produced by Chevron) was used. Axial load in the direction of an arrow A shown in the drawing was applied between the first test piece 30 and the inner ring 21 so that the contact surface pressure between the balls 22 and the first test piece 30 became equal to a predetermined value, and then the first test piece 30 was immobilized and the inner ring 21 was rotated at a rotation speed of 1200 min⁻¹. The passage speed of the balls 22 at this time was 3600 min⁻¹.

In the endurance test, as shown in FIG. 2, the contact surface pressure was intermittently raised so as to be 2.0 GPa at step S1, 2.6 GPa at step S2, 3.1 GPa at step S3, 3.5 GPa at step S4, and 4.1 GPa at step S5. At steps S1 to S5, the inner ring 21 was rotated 1×10⁷ times.

A method for the endurance test performed until peeling occurred on the diamond-like carbon coating of the second test piece will be shown below.

As shown in FIG. 3, in the testing device used for the endurance test performed until peeling occurred on the manganese phosphate coating 31 mentioned above, the test was conducted by using the second test piece 40 instead of the first test piece 30 as a test piece. That is, the second test piece 40 was placed in the container 25 so that the diamond-like carbon coating 41 (corresponding to the diamond-like carbon coating 6 b according to the invention) faced upward in the vertical direction, and the six balls 22 held by the cage 23 were placed on the diamond-like carbon coating 41, and then a test similar to the test of the first test piece 30 was conducted.

In FIG. 2, with regard to the manganese phosphate coating, peeling occurred when the contact surface pressure was 3.1 GPa, whereas, with regard to the diamond-like carbon coating, peeling occurred when the contact surface pressure was 4.1 GPa. From results of this test, it can be understood that the diamond-like carbon coating is more excellent in load bearing than the manganese phosphate coating.

FIG. 4 is a graph showing transitions in friction coefficients of the manganese phosphate coating and the diamond-like carbon coating under a no-lubricant condition.

A measurement method for the friction coefficients is as follows. A third test piece is a test piece in which a manganese phosphate coating is formed in a flat-plate test piece made of JIS SUJ2. Furthermore, a fourth test piece is a test piece in which a diamond-like carbon coating is formed on a flat-plate test piece made of JIS SUJ2.

A measurement method for transitions in the friction coefficient of the manganese phosphate coating of the third test piece will next be shown.

FIG. 5 is a schematic diagram showing a measuring device for measuring transitions in the friction coefficient. In this measuring device, balls 51 of 3/16 inch made of JIS SUJ2 and lubricating oil (not shown) were prepared.

A third test piece 60 was disposed so that a manganese phosphate coating 61 (corresponding to the manganese phosphate coating 6 a according to the invention) faced upward in the vertical direction, and the balls 51 fixed so as not to roll were placed on the manganese phosphate coating 61. Lubricating oil was applied to surface of the third test piece 60. As the lubricating oil, MEROPA WM320 in trade name (produced by Chevron) was used. An axial load of 10 N was applied between the third test piece 60 and the balls 51 so that the contact surface pressure became equal to 1.6 GPa. In this state, the balls 51 were moved relative to the third test piece 60 over a distance of 10 mm at an average linear speed of 40 mm/s. This relative movement was continued as reciprocal movement shown by arrows B in FIG. 5 for 3600 s.

A measurement method for transitions in the friction coefficient of the diamond-like carbon coating of the fourth test piece will next be shown.

As shown in FIG. 5, in the measuring device used in the measurement method for transitions in the friction coefficient of the manganese phosphate coating 61 described above, a test was conducted by using the fourth test piece 70 instead of the third test piece 60 as a test piece. That is, the fourth test piece 70 was placed so that the diamond-like carbon coating 71 (corresponding to the diamond-like carbon coating 6 b according to the invention) was in contact with the balls 51, and then measurement similar to the measurement on the third test piece 60 was conducted.

In FIG. 4, the friction coefficient of the manganese phosphate coating transitions in the range of 0.4 to 0.6, whereas the friction coefficient of the diamond-like carbon coating transitions below or at 0.2. From this result, it can be understood that the manganese phosphate coating is greater in friction coefficient than the diamond-like carbon coating.

With the cylindrical roller bearing 1 according to the embodiment of the invention described above, out of the inner ring raceway surface 3 a of the inner ring 3, which is a rotary ring, and the rolling contact surface 4 a of each cylindrical roller 4, one of the surfaces is provided with the manganese phosphate coating 6 a that is inferior in load bearing but great in friction coefficient, and the other surface is provided with the diamond-like carbon coating 6 b that is small in friction coefficient but excellent in load bearing. That is, on the inner ring raceway surface 3 a and the rolling contact surface 4 a, there are formed two kinds of coatings that cover each other's shortcomings. Therefore, due to the manganese phosphate coating 6 a, which is great in friction coefficient, slippage is less likely to occur between the inner ring raceway surface 3 a and the rolling contact surface 4 a, so that occurrence of smearing (a phenomenon in which a plurality of minute seizures is generated) can be effectively restrained. Furthermore, the diamond-like carbon coating 6 b, which is excellent in load bearing, hardens the surface, so that occurrence of peeling on the rolling contact surface 4 a provided with the coating 6 b can be effectively restrained. Therefore, it becomes possible to increase the service life of the cylindrical roller bearing 1.

Furthermore, since the manganese phosphate coating 6 a, which is great in friction coefficient, is formed on the inner ring raceway surface 3 a, the friction force of the manganese phosphate coating 6 a makes it possible to efficiently transmit rotary drive force of the inner ring 3 to the cylindrical rollers 4.

Note that, in the present embodiment, the rib surfaces 2 b 1 of the outer ring 2 as a fixed ring and the end surfaces 4 b of each cylindrical roller 4 are not surface-treated with coating. Therefore, increase in the sliding contact resistance between the rib surfaces 2 b 1 and the cylindrical rollers 4 due to coating can be prevented.

FIG. 6 is a sectional view showing a roller bearing according to a second embodiment of the invention. The present embodiment differs from the first embodiment in that rib surfaces are formed on an inner ring and that the rib surfaces and the end surfaces of cylindrical rollers are surface-treated with coating.

In the present embodiment, the outer periphery of the inner ring 3 has rib portions 3 b that are protruded radially outward at axially opposite sides of an inner ring raceway surface 3 a. Each rib portion 3 b has a rib surface 3 b 1 that is in sliding contact with a corresponding one of the end surfaces 4 b of each cylindrical roller 4.

The rib surfaces 3 b 1 of the inner ring 3 and the end surfaces 4 b of each cylindrical roller 4 are surface-treated with respectively different coatings. Specifically, a manganese phosphate coating 6 a is formed entirely over each rib surface 3 b 1. Furthermore, a diamond-like carbon (DLC) coating 6 b that contains, for example, a tungsten carbide carbon (WCC) is formed entirely over each end surface 4 b. The film thickness of each of the manganese phosphate coatings 6 a and the diamond-like carbon coatings 6 b is set equal to or less than 3 μm.

Similarly to the embodiment of the invention described above, since the inner ring raceway surface 3 a of the inner ring 3 and the rolling contact surface 4 a of each cylindrical roller 4 are surface-treated with the manganese phosphate coating 6 a and the diamond-like carbon coating 6 b, respectively, occurrence of smearing or the like on the inner ring raceway surface 3 a and the rolling contact surface 4 a can be effectively prevented, and therefore it becomes possible to increase the service life of the cylindrical roller bearing 1.

Furthermore, since the rib surfaces 3 b 1 of the inner ring 3 and the end surfaces 4 b of each cylindrical roller 4 are provided with two kinds of coatings that cover each other's shortcomings, due to the manganese phosphate coating 6 a, which is great in friction coefficient, the cylindrical rollers 4 are more likely to be rotated together with the inner ring 3 by the sliding contact resistance between the rib surfaces 3 b 1 and the end surfaces 4 b of the cylindrical rollers 4, so that rotary drive force of the inner ring 3 can be more efficiently transmitted to the cylindrical rollers 4. Furthermore, since the diamond-like carbon coating 6 b, which is excellent in load bearing, hardens the surface, occurrence of peeling on the end surfaces 4 b provided with the coatings 6 b can be effectively restrained.

Note that, the invention may be carried out with changes as appropriate, without being limited to the foregoing embodiments. For example, although in the foregoing embodiments, the manganese phosphate coating is formed on each of the outer ring raceway surface and the inner ring raceway surface and the diamond-like carbon coating is formed on each of the rolling contact surfaces of the cylindrical rollers, the diamond-like carbon coating may be formed on each of the outer ring raceway surface and the inner ring raceway surface and the manganese phosphate coating may be formed on each of the rolling contact surfaces of the cylindrical rollers.

Furthermore, although in the foregoing embodiments, coating is formed on each of the outer ring raceway surface and the inner ring raceway surface, it is only necessary to form coating at least on an inner ring raceway surface of a rotary ring.

Furthermore, although in the second embodiment, the manganese phosphate coating is formed on each rib surface and diamond-like carbon coating is formed on each of the end surfaces of the cylindrical rollers, the diamond-like carbon coating may be formed on each rib surface and the manganese phosphate coating may be formed on each of the end surfaces of the cylindrical rollers.

Furthermore although in the second embodiment, the diamond-like carbon coating is formed on each of the rolling contact surfaces and the end surfaces of the cylindrical rollers, the diamond-like carbon coating of the rolling contact surface of a cylindrical roller may be continuous with the diamond-like carbon coatings of the end surfaces of the cylindrical roller. Furthermore, a manganese phosphate coating may be formed on each of the rolling contact surfaces and the end surfaces of the cylindrical rollers. In this case, the manganese phosphate coating of the rolling contact surface of a cylindrical roller may be continuous with the manganese phosphate coating of the end surfaces of the cylindrical roller.

Furthermore, although in the second embodiment, a manganese phosphate coating is formed on each of the inner ring raceway surface and the rib surfaces of the inner ring, the manganese phosphate coating on the inner ring raceway surface of the inner ring and the manganese phosphate coating on each of the rib surfaces of the inner ring may be continuous with each other. Furthermore, a diamond-like carbon coating may be formed on each of the inner ring raceway surface and the rib surfaces of the inner ring. In this case, the diamond-like carbon coating on the inner ring raceway surface of the inner ring and the diamond-like carbon coating on each of the rib surfaces of the inner ring may be continuous with each other.

Furthermore, out of the diamond-like carbon coating and the manganese phosphate coating, one of the coatings may be formed on each of the inner ring raceway surface of the inner ring and the end surfaces of the cylindrical rollers, and the other coating may be formed on each of the rib surfaces of the inner ring and the rolling contact surfaces of the cylindrical rollers.

Furthermore, although in the second embodiment, the coating is formed over the entire end surfaces of each cylindrical roller, it is only necessary to form coating on at least a portion that is in sliding contact with a corresponding one of the rib surfaces.

Furthermore, although in each of the cylindrical roller bearings in the foregoing embodiments, the fixed ring is the outer ring, and the rotary ring is the inner ring, the fixed ring may be the inner ring and the rotary ring may be the outer ring.

Furthermore, the roller bearing is not limited to a radial cylindrical roller bearing, but may also be a thrust roller bearing or a tapered roller bearing.

DESCRIPTION OF REFERENCE CHARACTERS

-   1: CYLINDRICAL ROLLER BEARING (ROLLER BEARING) -   2: OUTER RING (FIXED RING) -   2 a: OUTER RING RACEWAY SURFACE (FIXED RACEWAY SURFACE) -   2 b 1: RIB SURFACE -   3: INNER RING (ROTARY RING) -   3 a: INNER RING RACEWAY SURFACE (ROTARY RACEWAY SURFACE) -   3 b 1: RIB SURFACE -   4: CYLINDRICAL ROLLER (ROLLER) -   4 a: ROLLING CONTACT SURFACE -   4 b: END SURFACE -   6 a: MANGANESE PHOSPHATE COATING -   6 b: DIAMOND-LIKE CARBON COATING 

The invention claimed is:
 1. A roller bearing, comprising: a fixed ring having a fixed raceway surface; a rotary ring having a rotary raceway surface that faces the fixed raceway surface; and a plurality of rollers rollably disposed between the fixed raceway surface and the rotary raceway surface, wherein: two different films are separately applied on the rotatory raceway surface and a rolling contact surface of each of the rollers, respectively, and one of the two different films is a manganese phosphate coating and an other of the two different films is a diamond-like carbon coating.
 2. The roller bearing according to claim 1, wherein: the film applied to the rotary raceway; surface is the manganese phosphate coating, and the film applied to the rolling contact surface of each of the rollers is the diamond-like carbon coating.
 3. The roller bearing according to claim 2, wherein: on the rotary ring, a rib surface that is in sliding contact with an end surface of each of the rollers is provided on at least one side of the rotary raceway surface in an axial direction; and out of the rib surface and the end surface of each of the rollers, one of the surfaces is provided with the manganese phosphate coating and the other surface is provided with the diamond-like carbon coating.
 4. The roller bearing according to claim 2, wherein the film thickness of the manganese phosphate coating and the diamond-like carbon coating is less than or equal to 3 μm.
 5. The roller bearing according to claim 1, wherein: on the rotary ring, a rib surface that is in sliding contact with an end surface of each of the rollers is provided on at least one side of the rotary raceway surface in an axial direction; and out of the rib surface and the end surface of each of the rollers, one of the surfaces is provided with the manganese phosphate coating and the other surface is provided with the diamond-like carbon coating.
 6. The roller bearing according to claim 1, further comprising: rib surfaces provided on both sides on the rotary raceway surface in an axial direction, wherein: each rib surface is in sliding contact with an end surface of the rollers, a first rib surface on one side of the rotary raceway surface covers an amount of surface area of the end surface of the rollers and a second rib surface on an other side of the rotary raceway surface covers an equal amount of surface area of the end surface of the rollers. 